1. Field of the Invention
This invention relates to a method of making a magnetic disk cartridge. This invention particularly relates to a method of making a magnetic disk cartridge comprising a small-diameter, very thin magnetic disk which is rotated at a high speed for recording and reproducing of image information or the like.
2. Description of the Prior Art
Floppy disks are widely used as recording media for computers because they are easy to handle and low in cost. The floppy disk comprises a disk-like base made of a flexible polyester sheet or the like, and magnetic material layers overlaid on opposite surfaces of the disk-like base. The floppy disk is rotated at a high speed for magnetically recording information in the magnetic material layers by use of a magnetic head.
On the other hand, by utilizing the aforesaid advantages of floppy disks and the advantages that a magnetic recording medium has over a silver halide photographic films in that the magnetic recording medium can be reused, it has been proposed to use a magnetic disk having a size smaller than the size of the floppy disks as an image recording medium in still cameras. The magnetic disk used for still cameras comprises a small-diameter, very thin magnetic recording medium, and a hub secured to the center of the magnetic recording medium. The magnetic disk is rotatably housed in a small-size, hard case provided at the center thereof with a hub hole for exposing the hub of the magnetic disk. The case also has magnetic head insertion apertures for exposing a part of the magnetic disk in the front surface and the rear surface of the case. The combination of the magnetic disk with the case is called a magnetic disk cartridge.
When the aforesaid magnetic disk cartridge is manufactured, it is necessary to secure the flexible magnetic recording medium to the hub. Conventionally, the step of securing the flexible magnetic recording medium to the hub has been carried out by one or the other of two methods as described below. In the first method, the magnetic recording medium is secured to the hub by ultrasonic fusion. However, in this method, since the cartridge of this type is made very small as described above, the area available for fusion of the magnetic recording medium with the hub becomes very small, and the magnetic recording medium and the hub are readily separated from each other during use of the cartridge. In the second method, a double-faced adhesive member comprising, for example, an nonwoven fabric and adhesive layers overlaid on opposite surfaces of the nonwoven fabric is positioned between the magnetic recording medium and the hub to secure the magnetic recording medium and the hub to each other.
In the case where the second securing method as described above is used, the hub is divided into an upper hub and a lower hub. The lower hub, the magnetic recording medium, the double-faced adhesive member, and the upper hub are positioned in this order from the bottom. Thus the upper hub and the magnetic recording medium are secured to each other by the double-faced adhesive member, and the upper hub and the lower hub are secured to each other by the double-faced adhesive member via a circular hole at the center of the magnetic recording medium. Or, the hub is fabricated integrally, and secured to the magnetic recording medium by the double-faced adhesive member. In any case, since the components of the cartridge are very small and since the magnetic recording medium is flexible, it is not always possible to secure the magnetic recording medium and the hub or hubs concentrically to each other.